The present invention relates to a burner unit for the flame treatment of flat textile materials and, more particularly, to a burner unit for singeing machines, with a combustion chamber terminating in a singeing slot supplied from a gas mixture chamber by two parallel burner slots, and with the gas mixture chamber being encased by a burner element including two approximately U-shaped profile members clamped together along their longitudinal edges with an interposition of a mixture distributing rail respectively delimiting the burner slots along a longitudinal side.
A primary difficulty in the singeing of textile fabrics resides in effecting complete uniform singeing over an entire area of the fabric, because even minor spatial or temporal fluctuations during the singeing action can lead to undesirable patterns, such as, for example, spotting or streaking of the fabric. Regular singeing presupposes a flame that is extremely uniform over its length and stable against disturbing influences, the length of the singeing flame generally amounting to several meters. However, the singeing flame is very greatly dependent, inter alia, on the way in which the gas mixture is fed into the combustion chamber.
As compared with older burner designs with mixture feed via a single burner slot, a burner unit such as, for example, dislosed in German Pat. No. 2,023,782 has proven to be extraordinarily effective, under practical conditions, wherein two burner slots, arranged in parallel to each other, are provided, ensuring a temporally and locally extensively uniform feeding of the singeing flame. In the conventional burner unit, the outwardly disposed longitudinal sides of the two burner slots are in each case formed by the longitudinal sides of approximately U-shaped profile members surrounding a mixture distributing rail, these profile members encompassing the gas mixture chamber. During the machining of the longitudinal edges by milling, grinding, or the like, these edges, due to the shape and size of the profile, are perforce located at a relatively great distance from the clamping sites on the work table or the like, so that an elastic yielding in front of the machining tool cannot be avoided. Consequently, marked limits are set for the machining accuracy, i.e. certain dimensional tolerances and undulations in the surface and, therefore, certain spatial residual fluctuations in the singeing flame must be tolerated.
The aim underlying the present invention resides in providing a burner unit of the type discussed above wherein an especially high uniformity of the singeing flame is achieved in its longitudinal extension.
According to this invention, the mixture distributing rail is encased between two guide strips, respectively defining the other longitudinal side of the burner slots, these guide strips being clamped together with the mixture distributing rail as a package between the two U-shaped profile members. The invention offers the advantage that in this structure both sides of the burner slots are constituted by strips that can be machined with a substantially higher precision and uniformity. Consequently, a high surface quality of the burner slots and thus a clean flow of the gas mixture can be achieved. Any waviness in the longitudinal direction, still unavoidable in the manufacture of the U-shaped profile members, is now no longer effective directly on the contour of the burner slots; rather, such waviness is transmitted, at most, to a markedly reduced extent due to the interposed guide strips.
According to a preferred embodiment, the guide strips can exhibit a narrow bulge on their outer side, upstream of the burner slots, and they are clamped between the two U-shaped profile members at the site of this bulge. Consequently, the guide strips are in contact with the U-shaped profile members, in this arrangement, only along a narrowly limited area which furthermore is clearly distant from the zone of the burner slots. Irregularities on the longitudinal edges of the U-shaped profile members can be transmitted to the guide strips only along this narrow area, and fade very quickly toward the rims of the guide strips. Due to this feature, the precision of the burner slots now depends exclusively on the machining quality of the guide strips and of the mixture distributing rail; as a result, burner slots of extreme precision can be manufactured which even with small slot widths of about 0.25 mm do not exhibit any detectable nonuniformities.
According to this invention, each guide strip can be provided with a fitting lug on its contact surface facing the mixture distributing rail, and this fitting lug can engage into a corresponding counter groove in the mixture distributing rail. The fitting lug can preferably exhibit a V-shaped cross section. The guide strips and the mixture distributing rail, combined into a package, are placed into an unequivocal position relatively to each other, which is of great importance particularly with regard to the front edges of the burner slots. If these are not arranged in exact opposition, considerable irregularities can occur in the flow pattern. Centering of the guide strips on the mixture distributing rail with the aid of V-shaped lugs permits a simple and yet very precise assembly and does not pose any special manufacturing problems.
According to another feature of the invention, the mixture distributing rail can have a rectangular cross section with the rail being provided on each longitudinal side with a pressure-equalizing groove respectively in communication with a burner slot. The mixture distributing rail can exhibit blind bores emanating from the inlet and oriented in parallel to the clamping surfaces, with a diameter of these bores corresponding approximately to half the thickness of the mixture distributing rail, and with these bores intersecting the pressure-equalizing grooves along a width of respectively about 1/5 of their diameter. The blind bores can terminate into an inlet groove, with a width of the latter being equal to the diameter of the blind bores. An advantage of this embodiment resides in that it is very simple to manufacture as compared with conventional structures. Since the blind bores directly intersect the pressure-equalizing grooves, heretofore customary cross bores can be omitted. However, a more important factor for the function of the burner unit is that the blind bores exhibit a relatively large diameter, that there is no abrupt transition between the inlet groove and the blind bores, and that the flow during transition from the blind bores to the pressure-equalizing grooves is only moderately deflected so that, in total, a very uniform flow through the mixture distributing rail is attained. The ensuing uniform supply to the burner slots is, beside the manufacturing accuracy of the burner slots, of great importance for keeping the singeing flame free of disturbances.
According to a further feature of the invention, the two sidewalls of the inlet groove can exhibit recesses that are approximately of the shape of a circular arc in cross section. These recesses effect, in the flow direction, initially a gradual cross-sectional flaring and thereafter a gradual cross-sectional narrowing. As a result, an additional smoothing of the flow in the inlet zone of the mixture distributing rail is achieved.